1. Field of the Invention
The invention relates to connectors for coaxial cable. More particularly the invention relates to cost effective connectors and a coaxial cable adapted for interconnection using axial compression along a cylindrical section formed at a peak of annular corrugation(s) in the outer conductor of the coaxial cable.
2. Description of Related Art
Transmission line cables employing solid outer conductors have improved performance compared to cables with other types of outer conductors such as metallic braid, foil, etc. Solid outer conductor coaxial cables are available in various forms such as smooth wall, annular corrugated, and helical corrugated. Smooth wall cable has the lowest materials cost but is relatively inflexible, limiting use of smooth wall cable where other than straight cable runs are required. Helical cable is flexible and relatively easy to securely terminate via connectors that thread into the helical cable corrugations. However, the helical cable profile also provides a path for water infiltration into the cable.
Annular cable is flexible and has improved resistance to water infiltration. Annular coaxial cables are typically terminated using connectors that incorporate a mechanical clamp between the connector and the lip of the outer conductor. The mechanical clamp assemblies are relatively expensive, frequently requiring complex manufacturing operations, precision threaded surfaces and or multiple sealing gaskets.
A relatively inexpensive alternative to mechanical clamp connectors is soldered connectors. Prior soldered connectors create an interconnection that is difficult to prepare with consistent quality and even when optimally prepared results in an interconnection with limited mechanical strength. Further, heat from the soldering process may damage cable dielectric and or sheathing material.
Another inexpensive alternative is interconnection by compression. Crimping is a form of compression where the compressive force is applied in a radial direction. Crimping a solid or stranded wire places a non-compressible core at the center of the crimp. This allows the crimp die to compress the connector body around the solid core at high pressure. The connector body is permanently deformed to conform to the solid mass of the wire, resulting in a strong mechanical and electrical bond. The strength of the bond in tension approaches the ultimate tensile strength of the wire. The absence of voids or air pockets in the crimp area prevents the migration of corrosive fluids within the interface. The high residual stress, in the material of the connector body, keeps the contact resistance low and stable.
Crimping braided outer conductors is more problematic. To prevent deformation of the outer conductors in relation to the center conductor, a support sleeve of one form or another may be used. Usually, the braid is captured in a layer between a tubular outer ferrule and the connector body. This crimp is not considered highly reliable. There are typically large voids in the interface allowing for corrosive degradation of the contact surfaces. The mechanical pull strength of the joint does not approach the strength of the wire. Finally, the connection allows relative movement between all 3 components, which results in a very poor, noisy electrical connection.
Due to the corrugation patterns used in solid outer conductor cables, tubular support sleeves would require a sleeve that significantly changes the internal dimensions of the cable, causing an RF impedance discontinuity. To prevent deformation of a solid outer conductor, without using an internal sleeve, an external mating sleeve adapted to key to the corrugation pattern has been used in a crimp configuration. However, the level of crimp force applicable before the outer conductor deforms is limited, thereby limiting the strength of the resulting interconnection.
Competition within the coaxial cable and connector industry has focused attention upon reducing manufacturing, materials and installation costs. Also, strong, environmentally sealed interconnections are desirable for many applications.
Therefore, it is an object of the invention to provide a method and apparatus that overcomes deficiencies in such prior art.